As shown in FIGS. 1(A)-1(C) and 2(A)-2(C), sealing means for packaging generally includes three-side-sealing (such as shown in FIGS. 1(A) and 2(A)), four-side-sealing (such as shown in FIGS. 1(B) and 2(B)), and back-side-sealing (such as shown in FIGS. 1(C) and 2(C)). Multirow three-side-sealing packaging machine has high automation and high efficiency, and therefore has become very popular. Traditional multirow three-side-sealing packaging machine comprises a film feeding unit, a dividing unit, a content feeding unit, a bag forming unit, a bag pulling unit, a longitudinally sealing unit, a transversally sealing unit and a cutting unit. The bag forming unit, as an important part of the packaging machine, has direct influence on the capability and performance of the packaging machine.
Patent application No. CN 96197906.2 disclosed a packaging machine with forming tube around which a ribbon of flexible material is wrapped, in order to shape a continuous sleeve, longitudinally sealed to obtain, with subsequent transversal sealings, filled and sealed packages, wherein it is equipped with a shaping device that produces on said sleeve, along the part between two transversal subsequent sealings, a gusset that is able to constitute the bottom structure of the package, that will have, when turned and placed over a horizontal ground, the necessary base to stand-up steadily in vertical position.
In this disclosure, the packaging film is provided to the forming tube directly from its rear. When the packaging machine is a multirow three-side-sealing packaging machine, i.e, when it has multiple forming tubes arranged in a first direction in sequence, one packaging film is divided into multiple packaging film straps simultaneously by the dividing unit, after which each of the multiple packaging film straps is provided to a respective forming tube from its rear, and then folded longitudinally. At this time, as shown in FIG. 3, longitudinal openings of the packaging films are facing a second direction that is perpendicular to the first direction, i.e., facing the front of the forming tube 1. Subjected to the folding direction and the longitudinal opening direction of the packaging films, it is necessary to provided a separate set of bag pulling unit, longitudinally sealing unit, transversally sealing unit and cutting unit for each of the packaging film straps, so as to carry out bag pulling, longitudinally sealing, transversally sealing and cutting. This makes it very hard for the multirow packaging machine to accomplish simultaneous bag pulling, longitudinally sealing, transversally sealing and cutting.
Since each separate bag pulling unit comprises two spindles and bag pulling rollers arranged on the spindles, it is necessary to provide synchronous control devices on all the spindles to ensure their synchronous operation, and therefore synchronous rotation of each pair of the bag pulling rollers, so as to achieve synchronous pulling of the multiple packaging films in the multirow packaging machine. For the same reason, it is necessary to provide corresponding synchronous control devices to achieve the longitudinally sealing, transversally sealing and cutting of the multiple packaging film straps. This leads to a complicated structure and high manufacturing cost of the packaging machine.